jafant...
I've driven my Thiels (2.2, 3.1, and currently 3.5's) with both tube and solid state amplifiers and have found that they are excellent with either. The one complaint I have with these "vintage" (minty!, in eBay parlance) designs is the speaker cabling, specifically where Thiel located the binding posts themselves. On the bottom!
This rules out using the "garden hose" variety of speaker cables since keeping them off of the floor proved to be problematic. I've used Goertz Alpha Core, Transparent Music Waves, and now I have AntiCables level 3 - which I've long been a fan of. That aside, very few loudspeakers have impressed me as much as Thiels do. My 3.5's are full range, 20hz - 20khz, and I've never used a subwoofer. They still continue to deliver outstanding sonics.
I think my favorite match up with mine was a Pass Labs X150.5, 150 watts into 8, 300 watts into 4 ohms which the Thiels are. My listening level is very conservative, and I've had fun listening with a McIntosh MC275 Mark VI tube amplifier, 75 watts per channel into virtually any load. Also a Rogue Audio Cronus Magnum integrated, 100 watts per channel. In retrospect I think I have to give the nod to the Pass Labs. Having all that extra headroom made me believe I was treating them right even if my listening level wouldn't stress a modest amp.
I've just purchased a Peachtree Audio 220SE integrated which will out put 350 watts into 4 ohms for the heck of it. (Pretty good deal direct from them.) I'm also looking at an Audio Research 300.2 amplifier - which is class T, capable of 500 watts per channel into 4 ohms.
One thing I will never do is part with my 3.5's again. The first pair I owned I gave to my nephew when I purchased a pair of Counterpoint Clearfield Metropolitans, an Alfred Von Schwiekert design. They were physically HUGE speakers. A few months ago I found another pair of the 3.5's right here not he gone and bought them without contacting the seller first. Regardless of price Thiels are some of the best loudspeakers out there. I love 'em. Good luck with yours!